When performing root canals, it is essential to drill into the root of the tooth all the way down to the apex. It is essential that the drilling terminate nearly exactly at the apex, as over-drilling through the apex may result in permanent damage to the tooth, and under drilling, or stopping before the apex, may not remove all of the necessary material, resulting in an increased chance for future infection.
Presently, while performing root-canals a dentist first measures the dept of the root to the apex by inserting a needle into the tooth and performing an X-ray. The height of the needle inserted within the tooth is noted and then added to the distance between the end of the needle and the apex in the X-ray. This combined height of the needle within the tooth and the distance from the apex is added together to get the total height of the root.
After the height of the root is determined, a visual stopper, such as rubber colored stopper, is positioned on the shank of the drill set in order to provide the dentist with a visual marking on the shank as to the height of the root to be drilled. The dentist then begins drilling the shank down into the root of the tooth until the stopper is flush with the top of the tooth.
There are several drawback associated with this method for performing root canals. Most importantly, the stopper or marker disposed on the shank does not act as a physical stopper but rather a visual indicator only prompting the dentist to stop drilling on their own. However, a number of occurrences can result in the dentist over drilling the root. For example, problems that could arise include but are not limited to: the dentist's hand or eyes may be fatigued after performing many root canals; the rubber stopper may move during drilling; the mouth may be small resulting in improper or insufficient lighting; the tooth may be chipped providing an uneven stopping point; the hole within the tooth may be too large to properly gauge when the stopper has reached the top of the tooth; or the angle of the handset may impair the dentist's view.
In each of these instances it is possible that the dentist may over drill or under drill the root, overshooting or undershooting the apex, causing lasting damage to the affected tooth.